Pidgin use to come with a GTK application in which you could select from any of the GTK themes and change your pidgin theme. For some reason unknown to me after pidgin 2.7 it started using a private GTK library and not using the GTK themes the way it did previously. I have only found this information by reading around the net and on the official pidgin wiki so if this info is incorrect I apologize. I am dissappointed by this as well as many people are Im sure because pidgin looks like garbage as an application. At work I use a mac and I have adium and it is much much much much nicer.